HOUSTON – Houston Grand Opera’s current pair of productions could hardly be in sharper contrast. Jerome Kern’s and Oscar Hammerstein’s Show Boat is alternating with Mozart’s and Da Ponte’s Don Giovanni.

Show Boat is the beginning of a series. In this and future seasons, Houston will be “reintroducing carefully selected American musical theater works that benefit from classically trained voices, a live, full-strength orchestra, and a fine chorus.”

In other words, “American musical, meet European grand opera.” Stephen Sondheim’s A Little Night Music will be next season’s musical, with others to follow in later years.

In the old days, such musical/opera pairings would probably have been met with scorn – remember how long it took for Porgy and Bess to reach the operatic stage? But opera audiences are much less snooty nowadays, and the snootiness level was just about undetectable at Saturday’s Show Boat performance.

There was one major flaw. Houston has decided to present Show Boat without projected supertitles, under artistic director Patrick Summers’ dubious assumption that “the work doesn’t need them.”

Well, it wouldn’t need them if acoustics and diction were flawless. But they weren’t, and about 50 percent of what was spoken and sung was unintelligible. Of course, the audience understood what was going on, but it was frustrating to miss so many lines that were meant to be grasped. The halls and lobby at intermission and after the show were filled with complaints. Houston might want to rethink this policy for future musicals.

Show Boat has a series of great hits, of course, and musically this performance was in pretty good shape. Joseph Kaiser’s Gaylord Ravenal seemed bland, but Melody Moore’s Julie, Sasha Cooke’s Magnolia and especially Marietta Simpson’s Queenie and Morris Robinson’s Joe scored points, as did the strong, unified singing of the chorus.

Francesca Zambello’s staging certainly didn’t soft-pedal the racial angle (Show Boat was a pioneer in focusing on America’s racial difficulties). The N-word was uttered a few times by racist characters, and the onstage showboat audience was segregated, as it would have been a century or more ago.

The sets by Peter J. Davison and costumes by Paul Tazewell were bright, a bit cartoonlike and evocative of late 19th- and early 20th-century America along the Mississippi.

Sunday’s Don Giovanni was musically pleasurable, though some characters seemed slightly out of character in light of Don Giovanni norms. For one thing, Adrian Eröd (Don Giovanni) has an exceptionally lyrical baritone voice, which may help explain why he seemed less menacing than typical.

On the other hand, Joel Prieto (Don Ottavio) has an exceptionally appealing lyric tenor voice, yet somehow he sidesteps the wimpy characteristic of so many Don Ottavios.

Conductor Trevor Pinnock led a well-paced performance by the Houston Grand Opera orchestra, and director Harry Silverstein, building on ideas by Göran Järvefelt, guided a staging that didn’t drift far from tradition. Decades-old sets and costumes are by Carl Friedrich Oberle.

The Houston Grand Opera has announced an impressive lineup for 2013-14. It includes Aida, Die Fledermaus, The Passenger by Mieczyslaw Weinberg, Rigoletto, A Little Night Music, A Coffin in Egypt by Ricky Ian Gordon, Das Rheingold (the beginning of a four-year-long Ring cycle) and Carmen.